1. Field of the Invention
After a medicine containing isotopes has been administered to a living body, the metabolic rate of the living body can be measured by measuring changes in concentration ratio of the isotopes. Accordingly, isotope analysis is utilized for disease diagnosis in the medical field.
The present invention is achieved with attention focused on the difference in light absorption characteristics of isotopes, and relates to a gas injection amount determining method in isotope gas analysis for measuring the concentration ratio of isotope gases, and also relates to isotope gas analyzing and measuring method and apparatus.
2. Description of Related Art
It is generally known that bacteria called Helicobacter pylori (HP) are present in the stomach as the cause of gastric ulcer and gastritis.
When HP is present in the patient's stomach, it is required to conduct a bacteria elimination treatment by administering an antibiotic substance. Accordingly, it is important whether or not HP is present in the patient. HP presents a strong urease activity and therefore dissolves urea into carbon dioxide and ammonia.
On the other hand, carbon includes isotopes of which mass number is 13 and 14, in addition to 12. Out of these isotopes, the isotope 13C having the mass number of 13 is not radioactive and is sable, thus causing the same to be readily handled.
In this connection, when urea marked with the isotope 13C is administered to a living body (patient), and the 13C concentration, more specifically the concentration ratio between 13CO2 and 12CO2, in the expired breath of the patient which is the final metabolic product, is measured, the presence/absence of HP can be made sure.
However, the concentration ratio between 13CO2 and 12CO2 in the natural world, is as high as 1:100. It is therefore difficult to precisely measure the concentration ratio in the expired breath of the patient.
Conventionally, it is known a method using infrared spectral diffraction as a method of obtaining the concentration ratio between 13CO2 and 12CO2 or the concentration of 13CO2 (See Japanese Patent Publication No. 61(1986)-42220(B)).
According to the method of Japanese Patent Publication No. 61(1986)-42220(B), there are prepared two, long and short, cells having lengths such that the 12CO2 absorption in one cell is equal to the 13CO2 absorption in the other cell, and lights having wavelengths suitable for respective analyses are irradiated to the respective cells, and the intensities of the transmitted lights are measured. According to this method, the light absorption ratio at the concentration ratio in the natural field can be made 1, and if the concentration ratio undergoes a change, the light absorption ratio varies according to this change. Thus, the change in concentration ratio can be known.
Even though there is adopted the method using infrared spectral diffraction above-mentioned, it is difficult to detect a slight change in concentration ratio.
According to the isotope gas analyzing and measuring method above-mentioned, the concentration of carbon dioxide 13CO2 is obtained with the use of a calibration curve which determines the relationship between absorbance and concentration of 13CO2. However, if the atmospheric pressure at which the calibration curve has been prepared, is different from the atmospheric pressure at which the absorbance of carbon dioxide 13CO2 is measured, such difference may cause an error of measurement of 13CO2 concentration.
Table 1 shows the results of measurement of CO2 concentration obtained in the following manner. That is, a predetermined volume of air having a predetermined CO2 concentration, was collected by a gas injection device at each of a plurality of atmospheric pressures, and was then injected into a cell. Each cell inside pressure was measured. Then, each absorbance was measured to measure the CO2 concentration. The calibration curve used at this time was prepared at an atmospheric pressure of 1005 hPa.
TABLE 1AtmosphericCellPressurePressure(hPa)(Mpa)CO2 Concentration10050.4022.9959640.3852.8748920.3572.5368580.3472.4457990.3232.245
According to Table 1, the cell inside pressures are naturally proportional to the atmospheric pressures, and the CO2 concentrations which must originally be constant, are lowered according to the reduction in atmospheric pressure. Thus, the concentration varies with the variations of the atmospheric pressure.
In measurement in which gas to be measured containing, as gas components, carbon dioxide 13CO2 and carbon dioxide 12CO2, is introduced into a cell, and in which the intensities of transmitted lights having wavelengths suitable for measurement of the respective gas components, are measured and then data-processed to measure the concentrations of the gas components, it is an object of the present invention to provide a gas injection amount determining method in isotope gas analysis, and isotope gas analyzing/measuring method and apparatus, each of which can correct concentration variations resulting from the atmospheric pressure variations, thus improving the measuring precision.